No abstract

We present an unprecedented copper(II)-assisted organic ligand fragmentation process under basic conditions leading to several ligands within three families of metallamacrocycle, Cu 6 , Cu 8 , and Cu 16 . The sequential multistep reaction include (i) the deprotonation of the starting alcohol, 1,2-bis(3,5-dimethyl-pyrazol-1-yl)ethane-1,2-diol (H 2 bdped) to its diolate bdped followed by complexation through six bonds (μ 6 ) to three copper atoms in a ring, (ii) the breaking of the ethane-pyrazole C−N bonds by the different solvent alcohols to form 1-(3,5-dimethyl-pyrazol-1-yl)-2-methoxyethane-1,2-diolate (dpmed) or 2-(3,5-dimethyl-pyrazol-1-yl)-2-hydroxyacetate (dpet), while retaining coordination to the copper centers and (iii) the final step to ethane-1,1,2,2-tetraolate, C 2 H 2 O 4 4− (et). Importantly, the latter product, only observed on two previous occasions, occupies the core of Cu 6 and Cu 16 through exceptionally eight coordination bonds (μ 8 ). Its alkyl esters, 2-alkoxyethane-1,1,2triolate (met, eet, and pet), also occupy the central parts of Cu 8 but forming six bonds (μ 6 ) instead. The other product, 3,5-dimethylpyrazolate (dp), acts as peripheral bridges (μ 2 ) but it is not involved in coordination if the starting salt is copper acetate, this may be a consequence of acetate being a better μ 2 -chelating ligand. In the presence of an oxidizing agent, K 2 Cr 2 O 7 , C 2 H 2 O 4 4− (et) is oxidized to oxalate, C 2 O 4 2− (ox). Thus, an additional μ 3hydroxide and μ 4 -oxalate in Cu 16 widen the complexity of the structures, not to mention the range of coordination geometries of the copper centers, though in the present cases they can be classed in only two types: distorted square-planar and square-pyramid. In addition to single-crystal crystallography, the results from different techniques such as IR, ESI-MS, optical UV−vis, and SQUID magnetometry help in the characterization of these rare metallamacrocycles made from unexpected and in situ generated ligands. We believe the results of the organic transformations are highly relevant to von Liebig's benzil−benzilic acid rearrangement.

The search for functional materials, for example those aiming at microelectronics, magnetic recording, and catalysis, often ventures into mixed metal systems to achieve optimization of the properties. Thus, understanding site preference and self-organization is crucial but hard to implement. Herein, we present a system whereby Mg II , Mn II , and Mn III ions selectively locate exact positions within the Brucitestructured cluster, Mn 13 Mg 6 , [Mn III ⊂Mg II 6 ⊂Mn II 9 Mn III 3 (L) 18 (OH) 12 (N 3 ) 6 ](ClO 4 ) 6 • 12CH 3 CN, HL = 1-(hydroxymethyl)-3,5-dimethylpyrazolate). The Mn III being small (78 pm) takes up the core position; while 6 Mg II (86 pm) are located in the inner ring, and the 9 large Mn II (97 pm) and 3 Mn III occupy the outer ring. The factors (a) ionic radii, (b) regularity in coordination geometry, oxophilicity, and softness of Mg II compared to Mn II , and (c) Jahn−Teller distortion of Mn III may all be implicated synergistically. Electrospray ionization mass spectrometry reveals the M 19 disc remains an integral unit when crystals are dissolved, and exchange between Mg and Mn occurs within the disc during its formation. Diamagnetic Mg II doping insulates the magnetic exchange between the central Mn III and those in the outer ring, thus giving an overall antiferromagnetic exchange interaction between nearest-neighbors of the outer ring. The work reveals the underlying rule for site-preference of main group metal versus transition metal in disc-like Brucite-structured cluster and provides an elegant new avenue to assemble heterometallic clusters in a stepwise fashion.

An unusual one-dimensional zig-zag hexanuclear Ni(ii) cluster has been easily and successfully constructed using a designed multidentate pyrazole-alcohol ligand.